New York Agricultural Experiment Station. 



219 



distinctly acid in reaction. These tests bear out the generally 

 admitted fact that media for soil work should have a reaction between 

 0.5 per ct. and 1.0 per ct. normal acid to phenolphthalein. 



Table VIII. — Tests to Determine the Effect of Varying the Reaction of 



ASPARAGINATE AGAR. 



* Tests Nos. 3 and 4 were made with different batches of media from the first two 

 tests. The media used in Nos. 3 and 4 contained 0.05 per ct. dextrose and 0.2 per ct. 

 asparaginate, instead of the usual amounts. 



TESTS COMPARING THE VARIOUS MEDIA. 



A series of tests was made comparing the soil extract gelatin and the 

 asparaginate agar with the other solid media that have been recom- 

 mended for soil bacteria. Table IX is a comparison between the 

 counts obtained upon the asparaginate agar and parallel counts 

 upon the soil-extract gelatin. In Tables X to XIII the counts 

 upon these two media are compared with those upon the media 

 recommended by Fischer, by Lipman and Brown, by Temple and by 

 Brown. 



In fifty-nine of the ninety-six comparative tests given in Table 

 IX, the soil-extract gelatin gave higher counts than the asparaginate 

 agar. In thirty-four cases the counts upon the agar were higher, 

 and in three cases both media gave the same count. These tests 

 show that the gelatin medium is rather better than the agar 

 medium if we judge by the number of soil bacteria that grow upon it. 

 In the matter of distinctions in appearance between colonies of 

 different bacteria, it has already been stated that the gelatin is the 

 more satisfactory; but the requirement of definite chemical com- 

 position is more nearly met by the agar. From these facts it may 

 be concluded that the gelatin is best for qualitative work, the agar 

 best for quantitative work. One other disadvantage of the gelatin, 

 its rapid liquefaction by certain organisms, constitutes a further 



